Orbitally controlled, sedimentary
cycles of the Newark Supergroup permit palyniferous Late Triassic sections to be
calibrated in time. Carnian palynofloras from the Richmond basin exhibit 2-m.y.
fluctuations in the spore/pollen ratio, but taxonomic composition remains stable.
Diversity of Norian and Rhaetian palynofloras increases prior to a 60% reduction at the
Triassic/Jurassic boundary. The extinction of Late Triassic palynomorph species is
coincident with a spike in the spore/pollen ratio and approximately synchronous with the
last appearances of tetrapod taxa and ichnofossil genera. This geologically brief episode
of biotic turnover is consistent with bolide impact hypotheses.

*Present address: 27
Tower Hill Avenue, Red Bank, New Jersey 07701

INTRODUCTION

The composition and diversity of Triassic faunas
and flo- ras are of particular interest with respect to the late Norian (=Rhaetian) mass
extinction, an event that culminated in a 42% decrease in the number of terrestrial
tetrapod families (Olsen et al., 1987) and a 23% reduction in diversity of marine
invertebrate families (Sepkoski, 1984). Although the Norian event is recognized as one of
the most severe Phanerozoic mass extinction episodes, substantial disagreement remains as
to the duration and synchroneity of the Late Triassic terrestrial and marine extinctions.

Multiple extinction events throughout the Carnian and Norian have been proposed for
both terrestrial tetrapods (Benton, 1986) and marine invertebrates (Benton, 1986; Johnson
and Simms, 1989). Hallam (1981) argued that the extinctions were concentrated in the
latter part of the Norian (=Rhaetian), but he maintained that the tetrapod turnover
preceded extinction of the marine invertebrates by several million years. Olsen et al.
(1987) provided evidence that Triassic vertebrate faunas persisted until the latest
Triassic.

Although these hypotheses make different predictions about the Late
Triassic fossil record, the dearth of Triassic/Jurassic boundary sections (Hallam, 1981),
the difficulty of correlating marine and terrestrial strata, and the proliferation of Late
Triassic time scales (see Kerp, 1991) render them difficult to test.

These problems can be partially surmounted in the Newark Supergroup of eastern North
America (Fig. 1). Sedimentation in these rift basins was continuous from the Carnian
through the Hettangian, and the Triassic/Jurassic boundary is accessible in five separate
basins. The presence of dated basalt horizons, in conjunction with periodic sedimentary
cycles, per- mits construction of a Late Triassic time scale calibrated in absolute time
(Fig. 2) (Fowell and Olsen, 1993). No marine strata are present, but the variety of
fossilized materials, including osseous tetrapod remains, palynomorphs, and vertebrate
ichnofossils, permits comparison of a suite of organisms preserved under diverse
conditions. In this chapter, we deal primarily with the palynological record. However, it
is hoped that the numerous tetrapod fossils and palynomorph-bearing horizons will
ultimately enable more rigorous correlations with global terrestrial and marine strata.

CYCLICITY

The Newark Supergroup is composed predominantly of fluvial and lacustrine strata that
fill a series of rift basins formed by the Pangean breakup. During the Late Triassic and
Early Jurassic, this chain of elongate half grabens stretched from 4°S to 15°N (Witte et
aI., 1991). Climate models for idealized geographic representations of Pangea have shown
that a large landmass centered on the equator will exhibit summer and winter monsoon
circulation patterns (Kutzbach and Gallimore, 1989; Short et al., 1991). These models are
consistent with the thick lacustrine deposits of the Newark Supergroup, where long-term
fluctuations of annual precipitation are indicated by the presence of hierarchical
transgressive and regressive lacustrine cycles (Olsen, 1986; Olsen et al, 1989).

The shortest of these cycles are shallowing-upward packages between 1.5
and 35 m thick, identified in outcrop on the basis of rock type and fabric (Olsen, 1986;
Olsen et al., 1989; Olsen, 1991). Using the rationale outlined by Olsen (1986), cycles
have been calibrated via biostratigraphic age estimates and published radiometric dates.
Biostratigraphic calibration and Fourier analysis of these cycles both yield an average
periodicity of approximately 21 k.y. (Olsen, 1986). This value falls between the 18-k.y.
and 21.5-k.y. precession periods calculated for the Early Jurassic (Berger et al., 1992).

Fourier analysis of long stratigraphic columns and cores of the entire Triassic Newark
basin section reveals higher-order cycles with periodicities of 100 k.y., 400 k.y., and 2
m.y. (Olsen, 1986). The l00 k.y. and 400 k.y. cycles correspond to periodicities predicted
by Milankovitch theory for the Earth's eccentricity cycles (Hays et al., 1976; Short et
al., 1991), which have remained relatively constant throughout Earth history (Berger and
Pestiaux, 1984). A 2-m.y. eccentricity cycle can also be shown to exist from the orbital
dynamics, but unlike the other cycles its effect on climate has not been modeled.

The regularity and duration of the Newark Supergroup lacustrine cycles are compatible
with the hypothesis that orbitally controlled seasonal and latitudinal variations in solar
radiation detennined the length and intensity of Mesozoic rainy seasons. A latitudinal
climatic gradient is also apparent; differences in the type and abundance of sedimentary
structures and facies indicate that southern Newark Supergroup basins were far more humid
than the northern basins (Hubert and Mertz, 1980; Olsen, 1991; Olsen et al., 1989). This
drier- to-the-north trend resulted in three primary types of lacustrine cycles
distinguishable by the ratio of wet/dry fabrics: the humid Richmond type, the dry Fundy
type, and the intermediate Newark type (Olsen, 1991). Palynologically productive horizons
are generally restricted to the deeper-water lacustrine facies. Consequently, the
completeness of the palynological record in stratigraphic sections from the Newark
Supergroup increases with the average lake depth.

Dry lacustrine cycles occur in the Fundy basin of Nova Scotia (Fig. I), where
sedimentation rates were so low that 21- k.y. cycles cannot be identified. Higher-order
cycles are manifested in the fonn of sand-patch cycles (Smoot and Olsen, 1985, 1988).
These cycles are approximately 1 to 2 m thick and consist of sedimentary fabrics that
record alterations between shallow, perennial lakes and playas with salt crusts (Olsen,
1991). Deep-water lacustrine facies are extremely rare, and preserved palynofloras are
similarly sparse.

Intermediate Newark-type cycles are present in the Dan River/Danville, Culpeper,
Gettysburg, Newark, Pomperaug, Hartford, and Deerfield basins (Fig. 1). These 21-k.y.
cycles display a range of sedimentary fabrics, from deep-water mi- crolaminae to subaerial
desiccation cracks. Many of the cycles contain deep-water facies, but shallow-water and
desiccated fabrics are more common (Olsen, 1991). Palynomorph preservation is restricted
to the deep-water facies and is discontinuous within individuaI 21-k.y. cycles.

Humid Richmond-type cycles are present in the Rich mond and Taylorsville
basins of the southern Newark Supergroup (Fig. 1). Desiccated, mudcracked fabrics are
rare, and 21-k.y. cycles consist primarily of microlaminated claystones, coals, and
shallow-water siltstones (Olsen, 1991). The nearly continuous palynological record of the
Richmond basin is ideal for studies of early Late Triassic microfloral diversity.

PALYNOFLORAL ASSEMBLAGES
AND SEDIMENTARY CYCLICITY
OF THE CARNIAN RICHMOND BASIN

Outcrops are rare in the Richmond basin, but a nearly complete palynological record has
been obtained from the 2,000-m-deep Horner #1 well (Fig. 3). Well cuttings of the entire
middle Carnian Richmond basin section, from the Otterdale Formation to the base of the
Tuckahoe Formation, were collected at 9.1-m (30-ft) intervals and processed for
palynomorphs..

In contrast to Early Jurassic palynomorph assemblages, which are dominated by a single
pollen genus (Corollina), the morphological and generic diversity of the Richmond
basin palynofloras is characteristic of Triassic assemblages through- out the Newark
Supergroup. Dominance of either bisaccate or monosaccate (circumsaccate) pollen
morphotypes is also typical. Spores, however, are far more abundant in the Carnian
Richmond basin assemblages than in Norian palynofloras from northern basins. The Horner #1
well cuttings exhibit large fluctuations in the relative abundance of pollen and spores
(Fig. 3) that appear to reflect the 2-m.y. climate cycle.

Well logs from Horner #1 indicate that the thickness of the 21-k.y. cycle increases
from 7 to 10 m downsection. Adjacent to the Horner #1 well, a 150-m outcrop of the Turkey
Branch Formation also exhibits an extremely regular, 7-m cycle thickness. Cores of
underlying formations confirm the presence of thicker, 10-m cycles. The average 21-k.y.
cycle thickness is estimated to be 8.5 m for the palynologically productive portions of
the Horner well. Application of this estimate to the data in Figure 3 demonstrates that
the Horner #1 well spans approximately 4 m.y. Peaks of the pollen/spore ratio, emphasized
by smoothing of the data in Figure 3, occur at ~2-m.y. intervals. The spores were produced
by lower vascular plants that favored high precipitation and/or humidity, whereas
pollen-producing seed plants dominated during intervals of relatively arid climate.

Despite periodic fluctuations in palynomorph abundances, the taxonomic composition of
the assemblages remains relatively stable throughout the entire Carnian record of the
Richmond basin. This indicates that the climatic variations produced gradual floral
changes and were not of sufficient magnitude to cause regional extinctions.

LATE TRIASSIC AND EARLY JURASSIC PALYNOFLORAS

The youngest sediments in the Richmond basin are of Carnian age, but the palynological
record is continued through Norian, Rhaetian, and Hettangian strata in basins to the
north. The Triassic/Jurassic boundary in these basins has been identified by the
appearance of palynofloras dominated by the circumpolloid pollen genus Corollina. This
Early Jurassic Corollina meyeriana palynoflora (Fig. 2) rapidly replaces the
diverse, monosaccate- and bisaccate-dominated assemblages characteristic of the Carnian,
Norian, and Rhaetian (Cornet, 1977; Cornet and Olsen, 1985).

The abrupt transition from Late Triassic to Early Jurassic palynofloras
is evident in Figure 4, a composite range chart of palynomorph species from deep-water,
lacustrine facies of the Culpeper, Gettysburg, Hartford, and Newark basins (see Table 1
for species names with citations). Temporal resolution of these ranges is derived from
Newark basin cyclostratigraphy. Fowell and Olsen (1993) use measured cycle thicknesses
from the Late Triassic and earliest Jurassic lacustrine record of the Newark basin to
calibrate the stratigraphic section in relative time (Fig. 2). This section is fixed in
absolute time by 202.2 ± 1.3 Ma 40 Ar/39 Ar dates (Sutter, 1988)
and 201 ± 1 Ma U/Pb dates (Dunning and Hodych, 1990) of the Palisades sill, which fed the
Orange Mountain basalt and the correlative Jacksonwald basalt (Ratcliffe, 1988).

The composite range chart in Figure 4 was constructed on the time-calibrated Newark
basin section using the graphic correlation method outlined by Shaw (1964). As
discontinuous preservation precluded calculation of continuous correlation lines from the
palynological data alone, correlation lines were fixed by paleontological, stratigraphic,
and palynological tie points (Fowell and Olsen, 1993).

Species' ranges for the late Carnian, Norian, and Rhaetian (Fig. 4; Table 1) indicate
that palynofloral diversity increased throughout the last 24 m.y. of the Triassic (see
Fig. 5 of Fowell and Olsen, 1993). The transition from diverse Triassic assemblages to Corollina-dominated
Jurassic palynofloras occurs at approximately 201 Ma and is coincident with a loss of
13 of the 20 most common Late Triassic species. In total, 24 of the 40 species recorded
from the latest Triassic palynofloras are absent from Early Jurassic assemblages. This
represents a 60% regional extinction across the Triassic/Jurassic boundary.

TRIASSIC/JURASSIC BOUNDARY SECTIONS

Palynomorph assemblages from exposures in the Jacksonwald Syncline of the Newark basin
further limit the Triassic/Jurassic boundary palynoflora! turnover to an 11-m interval
that is barren of palynomorphs. A local cycle thickness of ~20 m allows the duration of
this transition to be constrained to less than 21 k.y. (Fig. 5) (Fowell and Olsen, 1993).

Palynomorph assemblages characterized by unusually high percentages (>50%) of
trilete spores have been recovered from the Triassic/Jurassic boundary in three
Jacksonwald syncline sections (Fig. 5a, b, and c). All three sections lie within the
Passaic Formation, and two extend to the base of the ~201 Ma Jacksonwald basalt.
Stratigraphic correlations are facilitated by the cyclostratigraphy of the sections and
the presence in each of a black, organic-rich clay layer overlain by an unusual,
blue-gray, plant-bearing sandstone. Spore-dominated assemblages Cl, EVD, 6-4, and 6-5 are
composed of 50 to 89% trilete spore species of the genera Anapiculatisporites,
Converrucosisporites, Deltoidospora, Dictyophyllidites, Granulatisporites, Kyrtomisporis,
Porcellispora, Reticulatisporites, Todisporites, and Verrucosisporites (R.
Litwin, personal communication, 1989; Olsen et al., 1990). These palynofloras occur
between the highest Triassic assemblage (A4, Fig. 5a) and the lowest Jurassic Corollina
meyeriana palynoflora (EVC, Fig. 5b).

Palynofloras from section 6 (Fig. 5c) and the Exeter Village section
(Fig. 5b) serve to bracket the stratigraphic duration of the spore-dominated assemblages.
The percentage of trilete spores increases markedly between samples 6-2 and 6-4 of section
6 and decreases again from 6-5 to 6-6. The abundance of trilete spores also drops off
dramatically above sample EVD of the Exeter Village section.

In Figure 6, spore percentages from all productive localities in the Jacksonwald
Syncline are plotted against thickness above and below the base of the blue-gray
sandstone. The spore-dominated palynofloras have a limited stratigraphic distribution
(less than 0.5 m), apparently originating and terminating abruptly.

In the Grist Mills (Fig. 5a) and Exeter Village (Fig. 5b) sections, this spore spike
occurs above typical Late Triassic assemblages of monosaccates and bisaccates and below Corollina-rich
Jurassic palynofloras. This relationship is not apparent in section 6 (Fig. 5c).
Samples 6-1 and 6-2, which underline the spore spike, contain the high percentages of Corollina
typical of Jurassic assemblages. Yet these assemblages retain low abundances of the
monosaccate Triassic index species Vallasporites ignacii and Patinasporites
densus. The only comparable palynofloras in the Newark Supergroup are from the Fundy
basin, where samples with abundant Corollina and rare (but clearly not reworked) Patinasporites
densus are present 32 cm below the North Mountain basalt. This basalt has been
assigned a U/Pb date of 202 ± 1 Ma (Hodych and Dunning, 1992) and is correlative with the
Jacksonwald basalt. Given the low sedimentation rates in the Fundy basin (Olsen et al.,
1989; Olsen, 1991),the Fundy assemblages may be time-equivalent with samples 6-1
and 6-2. We consider these palynofloras indicative of uppermost Triassic strata due to the
presence of diagnostic Triassic species, which are absent from overlying assemblages in
both the Newark and Fundy basins.

DISCUSSION AND CONCLUSIONS

Evidence for a geologically rapid, terminal-Triassic biotic turnover in the Newark
Supergroup is not confined to the palynological record. Footprint assemblages from the
Jacksonwald Syncline show that the last appearances of the Late Triassic ichnofossil
genera Gwyneddichnium, Apatopus. Brachychirotherium. and two new genera are
coincident with the palynologically defined Triassic/Jurassic boundary (Silvestri, 1991;
Silvestri and Szajna, 1993). Absence of these five footprint taxa from Early Jurassic
assemblages corresponds to the disappearance of previously abundant tetrapod trackmakers
and constitutes a decrease of approximately 50% in the diversity of Newark basin
ichnofossil genera (Silvestri, 1991; Silvestri and Szajna, 1993).

Terrestrial tetrapod fossils of Late Triassic age are preserved
throughout the Newark Supergroup. However, no characteristic Triassic taxa are found among
abundant osseous remains from the earliest Jurassic strata of the Fundy basin. Calibration
of the ranges of the Late Triassic vertebrate families by lacustrine cycles indicates that
the last appearances of dominant Triassic taxa occurred within an interval of 850 k.y.
that brackets the Triassic/Jurassic boundary (Olsen et al., 1987).

The abruptness and apparent synchroneity of the tetrapod, ichnofossil,
and palynofloral extinctions in the Newark Supergroup are consistent with catastrophic
extinction scenarios involving volcanism or bolide impacts. Fowell and Olsen (1993)
previously rejected volcanism as a catalyst for Late Triassic palynological turnover in
the Newark Supergroup on the grounds that the first basalt flows lie 7 to 10 m above the
transition from Triassic to Jurassic palynomorph assemblages and ash-fall horizons have
not been observed.

Aspects of the Newark Supergroup palynofloral record are consistent with
a multiple-impact scenario. The presence of a geologically brief spore-spike above the
last appearances of Late 'Triassic palynomorph species is analogous to Cretaceous-Tertiary
boundary fern spikes (Tschudy et al., 1984; Tschudy and Tschudy, 1986; Nichols et al.,
1986; Fleming, 1990) hypothesized to represent a recolonization of ferns following
catastrophic destruction of the Cretaceous flora.

The presence of short-lived "transitional" assemblages, in which Corollina
is dominant but rare Late Triassic species persist (samples 6-1 and 6-2, Fig. 5c),
indicates possible disruption of the flora prior to the Triassic/Jurassic boundary
turnover. It is tempting to suggest a relationship between these palynofloras and one of
the lower shocked quartz horizons of Bice et al. (1992) and to correlate the spore-spike
with the uppermost shocked quartz layer and the extinctions of Triassic bivalves and
foraminifera. Such correlations are premature, however, and require better estimates of
sedimentation rates in the Tuscany section and evidence for shocked quartz in the Newark
basin sections. To date, a comprehensive search for shocked quartz in the Newark
Supergroup has not been completed, but we are currently conducting this crucial test of
the validity of the impact hypothesis.

Enhanced temporal resolution and accurate stratigraphic correlations are also essential
to future comparisons of Triassic/Jurassic boundary sections. Periodic sedimentary cycles
and good palynofloral preservation within the Newark basin allow temporal calibration of
Late Triassic palynofloral zones. Preliminary results are shown in Figure 2 and compared
to published chronostratigraphic time scales. Recently acquired cores of the entire
Triassic Newark basin section will permit refinement of the temporal data and better
resolution of the boundaries between palynofloral zones. It is hoped that the combination
of palynological and tetrapod data from the Newark Supergroup will eventually enable
correlation between our continuously calibrated Late Triassic time scale and global
sections with ammonite control.

ACKNOWLEDGMENTS

We thank S. Silvestri and R. Litwin for access to their unpublished data. We also thank
Superior Oil Company (now Mobil) for the funds to process the Horner #1 well samples and
R. Jones for accomplishing the bulk of the Horner well processing. We are grateful to A.
Traverse for sharing his laboratory during the initial phases of this study and providing
useful discussion. B. Coakley, A. Traverse, and an anonymous reviewer read the manuscript
and suggested changes that significantly improved it. Their time and effort is greatly
appreciated. This research was supported by a grant from the National Science Foundation
(EAR 89 16726).

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